efi/console: Implement getkeystatus() support

efi/console: Implement getkeystatus() support

Implement getkeystatus() support in the EFI console driver.

This is needed because the logic to determine if a key was pressed to make
the menu countdown stop will be changed by a later patch to also take into
account the SHIFT key being held down.

For this reason the EFI console driver has to support getkeystatus() to
allow detecting that event.

Note that if a non-modifier key gets pressed and repeated calls to
getkeystatus() are made then it will return the modifier status at the
time of the non-modifier key, until that key-press gets consumed by a
getkey() call.

This is a side-effect of how the EFI simple-text-input protocol works
and cannot be avoided.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>